Updating the boundary between the western Pampean ranges and the eastern Precordillera, province of San Juan

Abstract

An analysis is made of the fault system in the Tulum tectonic depression, situated in the southeastern part of the province of San Juan, which is in the arid western part of Argentina. The boundary of two morphostructural systems occurs in this valley: the eastern Andean Precordillera and the western Pampean ranges. In former studies it was found that this boundary runs along a fault system that crosses the Tulum depression with a NNE trends. The availability of new information from electric resistivity tests and wells drilled for ground water show that the metamorphic basement exposed in the Valdivia low, isolated mountain continues to the SSW thereof in the subsurface, as a structural high limited by faults on both flanks. Further south, the basement crops out again in the Salinas hill and continues in the shallow subsurface, as suggested by geomorphic features and geophysic and well data, along the same trend, as far as the Montecito. In this way, the Tulum fault system comes nearer the Precordillera and, at the Montecito hill, ends against the Las Peñas range, which is in the central Precordillera and is limited to the east by a fault of regional importance with Quaternary activity. The contact between the Pampean and Precordillera systems was found, then, to continue further south than shown in former studies and represents the surface and subsurface boundary of the Eastern Precordillera along all its length. This new structural information may be useful for exploring ground water and hydrocarbons.